Friction clutches are well known. Such clutches are typically spring-biased to an engaged position. This is a disadvantage in that the friction clutches are spring-biased under initial constant bias pressure which cannot be adjusted to varying conditions.
Such conventional clutches have the disadvantage that on movement from a disengaged position to an engaged position, they rely on the skill of the operator to smoothly re-engage the clutch.
Clutch disengagement devices are known whereby as a precondition of moving a shift lever, the disengagement device automatically disengages the friction clutch. Such known devices, however suffer the disadvantage that conditions for re-engagement are preset and do not vary to accommodate different drive and driven shaft conditions. Jerky shifting, engine stalling and excessive clutch wear can result producing possible hazardous situations when used in passenger vehicles.